What kind of ad are you trying to place, a WTB or selling your other surround sound? You can absolutely run 3 P163s up front, but I'd opt for the center if you can afford it.
Something else to consider though, if you are going to use speaker stands, bookshelf speakers are going to take up just as much, if not more room than the floorstanding speaker. Plus the bass extension of the P363 will let you get by without a sub and still have good bass.